1. Field Of The Invention
The present invention relates to loudspeaker systems for sound reproduction. More particularly, the present invention relates to stereophonic loudspeaker systems having enhanced bass response.
2. Description Of The Prior Art
The art of sound reproduction involves capturing sounds such as music, processing the sounds, and reproducing the captured sounds in aural form. Processing may be primarily amplification, as in a public address system, or it may also include recording the sound in a fixed form, such as a magnetic tape, grooved disc or optically read disc and playing back the recorded sound from the fixed form. Processing may also include broadcast and reception of a signal representing the sound by radio or television.
In the art of sound reproduction, each step of the processes of capturing, processing and reproducing the captured sounds results in a loss in the accuracy of the reproduction of the sound. This accuracy of sound reproduction may be measured by various parameters, but is referred to generally as "fidelity." The development of the modern art of sound reproduction has been spurred by a continuing quest for increasing levels of sound fidelity coupled with a quest for aurally pleasing sound reproduction.
One key element in sound reproduction is a loudspeaker system that converts electrical signals representative of the sound to be produced into aurally perceptible sound. The loudspeaker system is particularly important in producing high fidelity and aurally pleasing sound as it is typically the final element in the sound reproduction system. A loudspeaker system typically includes one or more loudspeaker enclosures, each loudspeaker enclosure having one or more electrosonic transducers, or "drivers", mounted in the enclosure.
A limiting factor in the ability of a loudspeaker system to contribute to high fidelity and aurally pleasing sound reproduction is its ability to produce low frequency sounds pleasingly. Typically the ability of a loudspeaker system to reproduce low frequency sounds pleasingly is determined in large part by the physical size of the drivers and the enclosure. Generally, larger drivers and enclosures produce more pleasing low frequency sounds than smaller drivers and enclosures. In practical loudspeaker system design, however, the desirability of large drivers and enclosures for pleasing low frequency sound reproduction is balanced by a desirability of smaller drivers and enclosures for use in the limited space available in homes, automobiles, and other places where loudspeaker systems are typically used. The ability of the loudspeaker system to produce pleasing low frequency sounds is further affected by the size, geometry, materials and other characteristics of the room or other place in which the loudspeaker system is used.
Many loudspeaker designs have been proposed to improve the fidelity and aurally pleasing qualities of sound reproduction within loudspeaker systems of a practical physical size. Angled front baffles are seen in U.S. Des. No. 210,382 to T. Lane, and in U.S. Des. No. 222,477 to H. Wada, et al. Ducted ports are seen in U.S. Pat. No. 3,952,159 to W. Schott, and in U.S. Pat. No. 4,688,864 to R. Guss. Ports which perform structural as well as acoustic functions are seen in U.S. Pat. No. 4,201,274 to C. Carlton. Still another port or vent for use with bass range loudspeakers is seen in U.S. Pat. No. 4,284,166 to G. Gale.
Bass range drivers mounted in a bottom wall of a loudspeaker enclosure rather than in a front baffle, and which are electrically driven by an amplifier are seen in Guss and in U.S. Pat. No. 3,867,996 to N. Lou, as well as in U.S. Pat. No. 4,134,471 to D. Queen. None of the prior art mounts a bass range driver complete with all of its electromagnetic components in an opening of a loudspeaker enclosure without connecting the driver to the amplifier electrical output. None of the prior art patents, the commercial devices available, or the literature on the construction of loudspeaker enclosures appear to suggest any use of openings or vents of different types together in a loudspeaker enclosure.
Duct tubes in place of simple openings are also known in the construction of bass reflex loudspeakers. Such tubes are located entirely within the enclosure or backchamber of bass range loudspeakers. A bass range duct tube providing air or sound communication between the backchamber of a loudspeaker enclosure to an opening in a loudspeaker mounting baffle plate does not appear to be known. Further, passing the tube through a second backchamber or subenclosure which contains and isolates higher mid and high frequency range loudspeakers does not appear to be known in the prior art.
Two divergent means of reducing enclosure volume while maintaining relatively high levels of acoustic output at low frequency may be seen in R. Guss, U.S. Pat. No. 2,993,091. The Guss device involves multiple loudspeakers arranged so as to physically increase the acoustic drag on each diaphragm as a function of the movement of the multiple diaphragms of the several loudspeakers. In addition to Guss, U.S. Pat. No. 4,146,745 to T. Froeshle, et al., employs multiple loudspeakers sharing common vent tubes. In T. Froeshle the diaphragms of the loudspeaker do not share the enclosure backchamber. The loudspeakers are energized by the amplifier electrical output during operation.
A third attempt to reduce enclosure volume is cited by R. Guss as background to his invention. This invention employs a dynamic cone driver to damp the motion of the diaphragm of a similar loudspeaker by locating it within the enclosure, closely placed behind the driver to be damped. This damping driver is neither electrically energized, nor exposed to the ambient atmosphere surrounding the device. Rather the loudspeaker is sealed within the enclosures.
Other references of, general interest include U.S. Pat. No. 3,688,864 to T. Froeschle, et al. and U.S. Pat. No. 4,146,745 to R. Guss.
It is against this background that the bass-enhancing loudspeaker system of the present invention developed.